CORROSION |
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Stress Corrosion Corrosion Fatigue Fretting Corrosion Heat Treatment |
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Chemical treatments.
Parco Lubrizing. Parco lubrizing is a chemical treatment for iron and steel parts which converts the surface to a nonmetallic oil-absorptive phosphate coating. It is designed primarily to reduce wear on moving parts. The process is a modification of parkerizing, and consists a precleaning treatment in which vapor degressing, acid pickle, or spray emultion is used, followed by 15- minute dip in solution of water and 10 percent by volume of Parco Lubrite. This is followed by a water rinse and a dip in watersoluble oil. The phosphate surface soaks up oil and retains it Anodizing. Anodizing is the most common surface treatment of nonclad aluminum alloy surfaces. The aluminum alloy sheet or casting is the positive pole in and electrolytic bath in which chromic acid or other oxodizing agent produces an aluminum oxide film on the metal surface. Aluminum oxide is naturally protective, and anodizing merely increases the thickness and density of the natural oxide film. When this coating is damaged in service, it can only be partially restored by chemical surface treatments. Therefore, any processing of anodizid surfacess, including corrosion removal, should avoid unnecessary destruction of the oxide film. The anodized coating provides excellent resistance to corrosion. The coating is soft and easily scratched, making it necessary to use extreme caution when handling it prior to coating it with primer. Aluminum wool, nylon webbing impregnated with aluminum oxide abrasive or fiber bristle brushes are the approved tools for coating anodized surfaces. The use of steel wool, steel wire brushes, or harsh abrasive materials on any aluminum surfaces is prohibited. Producing a buffed or wire brush finish by any means is also prohibited. Otherwise, anodized surfaces are treated in much the same manner as other aluminum finishes. In a addition to its corrosion resistant qualities, the anodic coating is also an excellent bond for paint. In most cases parts are promed and painted coating is a poor conductor of electricity : therefore, if parts require bonding, the coating is removed where the bonding wire is to be attached. Alclad surfaces that are to be left unpainted require no anodic treatment : it is usually anodized to provide a bond for the paint. Alodizing. Alodizing is simple chemical treatment for all aluminum alloys to increase their corrosion resistance and improve their paint-bonding qualities. Becouse of its simplicity, it is rapidly replacing anodizing in aircraft work. The process consists of precleaning with an acidic or alkaline metal cleaner that is applied by either dipping or spraying. The parts are then rinsed with fresh water under pressure fot 10 to 15 seconds. After thorough rinsing, alodine is applied by dipping, spraying, or brushing. A thin, hard coating results which ranges in color from light, bluish-green with a slight irdescence on copperfree alloys to an olive green on copper-bearing alloys. The alodine is first rinsed with clear, cold or warm water for a priod of 15 to 30 seconds. An additional 10-to15-second rinse is then given in a deoxylyte bath. This bath is to counteract alkaline material and to make the alodyzed aluminum surface slightly acid on drying. Chemical Surface Treatment and Inhibitors. As previously described, aluminum and magnesium alloys in particular are protected originally by a variety of surface treatments. Steel may have been Parco Lubrized or otherwise oxidized on the surface during manufacture. Most of these coatings can only be restored by processes which are completely impractical in the field. But, corrode areas where such protective films have been destroyerd require some type of treatment prior to refinishing. The following inhibiting materials are particularly effective in the field treatment of aluminum, are beneficial to bare magnesium, and are of some value even on bare steel parts. |
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| Corrosion of ferrous metals. | ||
| One of the most familiar types of corrosion is ferrous oxide,.. | ||
| Corrosion of aluminum and aluminum alloys. | ||
| Corrosion attack on aluminum surfaces is usually quite obvious, | ||
| Corrosion of magnesium alloys. | ||
| Magnesium is the most chemically active of the metals used,. | ||
| Treatment of titanium and titanium alloys. | ||
| Attack on titanium surfaces is generally difficult to detect | ||
| Protection of dissimilar metal contacts. | ||
| Certain metals are subject to corrosion when placed in contact with other metals | ||
| Processes and materials used in corrosion control. | ||
| Aircraft parts are almost always given some type surface finish | ||
| Chemical treatment. | ||
| Parco Lubrizing in a chemical treatment for iron and steel parts | ||
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Copyright @ 2007. |
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